Banco Ambrosiano was an Italian bank that collapsed in 1982. At the centre of the bank's failure was its chairman, Roberto Calvi and his membership in the illegal Masonic LodgePropaganda Due (aka P2). Vatican Bank was Banco Ambrosiano's main shareholder, and the death of Pope John Paul I in 1978 is rumored to be linked to the Ambrosiano scandal. Vatican Bank was also accused of funneling covert United States funds to Solidarity and the Contras through Banco Ambrosiano.

Roberto Calvi, general manager of Banco Ambrosiano since 1971, appointed chairman from 1975 to his death in June 1982. He was often referred to as "God's Banker" because of his close financial ties with the Vatican.

The Banco Ambrosiano was founded in Milan in 1896 by Giuseppe Tovini, a Catholic advocate in Valle Camonica, and was named after Saint Ambrose, the fourth century archbishop of the city. Tovini's purpose was to create a Catholic bank as a counterbalance to Italy's "lay" banks, and its goals were "serving moral organisations, pious works, and religious bodies set up for charitable aims." The bank came to be known as the "priests' bank"; one chairman was Franco Ratti, nephew to Pope Pius XI. In the 1960s, the bank began to expand its business, opening a holding company in Luxembourg in 1963 which came to be known as Banco Ambrosiano Holding. This was under the direction of Carlo Canesi, then a senior manager, and from 1965 chairman.

In 1967, Canesi brought Roberto Calvi into Ambrosiano. In 1971, Calvi became general manager, and in 1975 he was appointed chairman. Calvi expanded Ambrosiano's interests further; these included creating a number of off-shore companies in the Bahamas and South America; a controlling interest in the Banca Cattolica del Veneto; and funds for the publishing house Rizzoli to finance the Corriere della Sera newspaper (giving Calvi control behind the scenes for the benefit of his associates in the P2 masonic lodge). Calvi also involved the Vatican Bank, Istituto per le Opere di Religione, in his dealings, and was close to Bishop Paul Marcinkus, the bank's chairman. Ambrosiano also provided funds for political parties in Italy, and for both the Somoza dictatorship in Nicaragua and its Sandinista opposition. There are also rumours that it provided money for Solidarity in Poland (it has been widely alleged that the Vatican Bank funded Solidarity).

Calvi used his complex network of overseas banks and companies to move money out of Italy, to inflate share prices, and to secure massive unsecured loans. In 1978, the Bank of Italy produced a report on Ambrosiano that predicted future disaster and led to criminal investigations. However, soon afterward the investigating Milanese magistrate, Alessandrini, was killed by a left-wing terrorist group, while the Bank of Italy official who superintended the inspection, Mario Sarcinelli, found himself imprisoned on charges that were later dismissed.

In 1981, police raided the office of Propaganda Due Masonic lodge to apprehend the Worshipful MasterLicio Gelli, and uncover further evidence against Roberto Calvi. Calvi was arrested, put on trial, and sentenced to four years in prison. However, he was released pending an appeal and retained his position at the bank. Other alarming developments followed: Carlo de Benedetti of Olivetti bought into the bank and became deputy chairman, only to leave two months later after receiving Mafia threats and lack of co-operation from Calvi. His replacement, a longtime employee named Roberto Rosone, was wounded in a mafia shooting incident. The criminal organization responsible for this shooting was the Banda della Magliana (Magliana Gang) which had taken over Rome's underworld in the late 1970s, and has been related to various political events of the anni di piombo (years of lead).

In 1982, it was discovered that the bank was unable to account for $1.287 billion (equivalent to $3.15 billion in present day terms). Calvi fled the country on a false passport, and Rosone arranged for the Bank of Italy to take over. Calvi's personal secretary, Graziella Corrocher, left a note denouncing Calvi before leaping to her death from her office window. Calvi's body was found hanging from Blackfriars Bridge in London on June 18 (see death of Roberto Calvi).

During July 1982, funds to the off-shore interests were cut off, leading to their collapse, and in August the bank was replaced by the Nuovo Banco Ambrosiano under Giovanni Bazoli. There was much argument over who should take responsibility for losses incurred by the Old Ambrosiano's off-shore companies, and the Vatican eventually agreed to pay out a substantial sum without accepting liability.

In April 1992, Carlo De Benedetti, former deputy chairman of Banco Ambrosiano, and 32 other people were convicted of fraud by a Milan court in connection with the bank's collapse.[2] Benedetti was sentenced to six years and four months in prison,[2] but the sentence was overturned in April 1998 by the Court of Cassation.[3]

Just before the media revealed the Ambrosiano scandal, Gérard Soisson, manager of transaction clearing company Clearstream, was found dead in Corsica, two months after Ernest Backes's dismissal from Clearstream in May 1983. Banco Ambrosiano was one of the many banks to have un-published accounts in Clearstream. Backes, formerly the third highest-ranking officer of Clearstream and a primary source for Denis Robert's book on Clearstream's scandal, Revelation$, claims he "was fired because (he) knew too much about the Ambrosiano scandal. When Soisson died, the Ambrosiano affair wasn't yet known as a scandal. (After it was revealed) I realized that Soisson and I had been at the crossroads. We moved all those transactions known later in the scandal to Lima and other branches. Nobody even knew there was a Banco Ambrosiano branch in Lima and other South American countries." [6] As of 2005, while the Italian justice has opened up again the investigation concerning the murder of Roberto Calvi, Ambrosiano's chairman, it has asked the support of Ernest Backes, and will investigate Gerard Soisson's death, according to Lucy Komisar. Licio Gelli, headmaster of P2 masonic lodge, and mafioso Giuseppe "Pippo" Calò, are being prosecuted for the assassination of Roberto Calvi.

France denied deliveries of Exocet AM39 missiles purchased by Peru to avoid the possibility of Peru giving them to Argentina, because they knew that payment would be made with a credit card from the Central Bank of Peru, but British intelligence had detected that the guarantee was a deposit of two hundred million dollars from the Banco Ambrosiano Andino, an owned subsidiary of the Banco Ambrosiano.[7][8]

Journalist David Yallop believes that Calvi, with the assistance of P2, may have been responsible for the death of Albino Luciani who, as Pope John Paul I, was planning a reform of Vatican finances. This is one of many conspiracy theories about Luciani, who died of a heart attack. However, Calvi's family maintains that he was an honest man manipulated by others. Their perspective informs Robert Hutchison's 1997 book Their Kingdom Come: Inside the Secret World of Opus Dei. According to the magistrates who indicted Licio Gelli, P2's headmaster, and Giuseppe Calò for Calvi's murder, Gelli would have ordered his death to punish him for embezzlement of his and the mafia's money, while the mafia wanted to stop him from revealing the way Calvi helped it in money laundering.